Redefining Ventricular Access Landmarks: A Novel Approach Using Magnetic Resonance Imaging and 3-Dimensional Reconstructions for Keen's Point Trajectories.

Background: Cerebrospinal fluid diversion via shunt placement is a common neurosurgical intervention. Keen's Point is a widely used landmark for accessing the trigone of the lateral ventricle; however, it lacks clinical validation. This study re-evaluates Keen's Point scalp parameters using magnetic resonance imaging (MRI) to identify an ideal shunt entry point based on 3-dimensional reconstructions.

Methods: MRI data from 36 Parkinson disease patients scheduled for deep brain stimulation were analyzed. The optimal ventricular puncture site (A Point) was identified on axial MRI images and mapped to the scalp. Distances from A Point to a perpendicular line from the external auditory meatus (B Point) and from B Point to the pinna and external auditory meatus were measured. The Posterior Callosal Angle (PCA) was calculated to assess its correlation with the distance between A and B points. Statistical analysis used regression and t-tests (P < 0.05).

Results: After excluding patients with PCA outside 70°-100°, 24 patients remained. The optimal distance from B Point to A Point significantly increased from 25-30 mm (as described by Keen) to 56.89 ± 1.36 mm (P < 0.01). Average PCA angle (85°) correlates with a distance of ∼57 mm, and a significant negative correlation was found between PCA and the distance from A Point to B Point (r = -0.42, P < 0.03).

Conclusions: This modified Keen's Point is a reliable landmark for ventriculostomy. Incorporating PCA into preoperative planning enhances catheter placement accuracy, providing a prominent approach to shunting at Keen's Point.